Heat Pump With A Storage Tank

ABSTRACT

A device includes a storage tank and a heat pump including at least one condenser, an expansion valve, an evaporator, and a compressor. The heat pump includes a working circuit for a circulating working fluid. The storage tank is arranged between the condenser and the evaporator with respect to the working circuit, and the storage tank includes a piston and/or a membrane for controlling a fluid level of the working fluid in the condenser.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2015/051138 filed Jan. 21, 2015, which designates the United States of America, and claims priority to DE Application No. 10 2014 203 578.3 filed Feb. 27, 2014, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a device and a method for regulating a fluid level of a working fluid of a heat pump.

BACKGROUND

Fluids are typically used as working means (working fluids) in refrigerating machines, in particular in heat pumps. The working fluid hereby circulates within a working circuit of the heat pump. When the heat pump is started up, the working fluid is typically fed into the working circuit of the heat pump and hence fills the heat pump.

In heat pumps known from the prior art, the working circuit of the working fluid is closed during the operation of the heat pump. In other words, the working fluid of the heat pump circulates within a closed working circuit. As a result, it is not possible to exert any influence on the working circuit of the working fluid, in particular on temperature changes of the working fluid. Any leaked working fluid is replaced only during maintenance work on the heat pump which generally takes place once a year. However, the heat pump is not operational during maintenance work.

Heat pumps generally discharge the heat received from a heat source to a heat sink. Fluctuations in the temperature of the heat sink, and in the temperature of the heat source, can hereby occur. Known heat pumps are able to react only inadequately to temperature fluctuations of the heat sink and/or the heat source. In particular, the efficiency (coefficient of performance, COP) of the heat pump is reduced by such temperature fluctuations, depending on the use.

SUMMARY

One embodiment provides a device comprising a storage tank and a heat pump, said heat pump having at least a condenser, an expansion valve, an evaporator, and a compressor, wherein the heat pump comprises a working circuit for a circulating working fluid, wherein the storage tank is arranged, with respect to the working circuit, between the condenser and the evaporator, and the storage tank comprises a piston and/or a diaphragm for regulating a fluid level of the working fluid in the condenser.

In one embodiment, the storage tank comprises a piston and is fluidically coupled to the heat pump via an outlet and inlet valve, wherein the outlet valve, with respect to the working circuit, is arranged between the condenser and the expansion valve, and the inlet valve is arranged between the expansion valve and the evaporator.

In one embodiment, the storage tank is designed as a hydraulic cylinder.

In one embodiment, the outlet and/or inlet valve comprises a further expansion valve and a non-return valve.

In one embodiment, the storage tank is designed as a collecting tank, and comprises a diaphragm, wherein the collecting tank is arranged, with respect to the working circuit, between the condenser and the expansion valve.

In one embodiment, the collecting tank is coupled to an air compressor, wherein the air compressor is designed to feed compressed air into a partial volume, delimited by the diaphragm, of the collecting tank.

In one embodiment, the partial volume, delimited by the diaphragm, of the collecting tank is coupled to a compressed-air outlet valve.

In one embodiment, the collecting tank has a displacement unit which is designed to mechanically displace the diaphragm.

Another embodiment provides a method for operating a heat pump with a working fluid circulating within a working circuit, in which the working fluid is condensed by means of a condenser, is expanded by means of an expansion valve, is evaporated by means of an evaporator, and compressed by means of a compressor, in which the working fluid, with respect to the working circuit, is guided between the condenser and the evaporator to a storage tank, wherein a fluid level of the working fluid in the condenser is regulated by means of a piston and/or a diaphragm of the storage tank.

In one embodiment, the fluid level is regulated by means of the piston and in which the working fluid is guided to the storage tank, with respect to the working circuit 42, between the condenser and the expansion valve by means of an outlet valve.

In one embodiment, the working fluid is guided, with respect to the working circuit, between the expansion valve and the evaporator by means of an inlet valve from the storage tank back to the heat pump, wherein the outlet valve is closed.

In one embodiment, the storage tank is designed as a collecting tank, in which the fluid level is regulated by means of the diaphragm, and in which the working fluid is guided, with respect to the working circuit, between the condenser and the expansion valve to the collecting tank.

In one embodiment, a first and/or second partial volume, delimited by the diaphragm, of the collecting tank is enlarged or reduced by a mechanical displacement of the diaphragm.

In one embodiment, the fluid level of the working fluid is regulated if the fluid level of the working fluid in the condenser exceeds or falls below a threshold value.

In one embodiment, the fluid level of the working fluid is regulated if the temperature of the working fluid exceeds or falls below a threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

Example aspects and embodiments of the invention are described in detail below with reference to the drawings, in which:

FIG. 1 shows a heat pump with a storage tank which is designed as a hydraulic cylinder; and

FIG. 2 shows a heat pump with a collecting tank which comprises a diaphragm for regulating the fluid level.

DETAILED DESCRIPTION

Embodiments of the present invention may enable adaptation of a heat pump to temperature fluctuations of a heat sink.

Some embodiments provide a device comprising a storage tank and a heat pump, said heat pump having at least a condenser, an expansion valve, an evaporator and a compressor, wherein the heat pump comprises a working circuit for a circulating working fluid, wherein the storage tank is arranged, with respect to the working circuit, between the condenser and the evaporator, and the storage tank comprises a piston and/or a diaphragm for regulating a fluid level of the working fluid in the condenser.

By virtue of the disclosed arrangement of a storage tank, which comprises a piston and/or a diaphragm, in the working circuit of the heat pump, the fluid level of the working fluid in the condenser of the heat pump can advantageously be regulated. The fluid level of the working fluid in the condenser of the heat pump is hereby regulated by the piston, for example by a translational movement of the piston, and/or by a displacement and/or deformation of the diaphragm in the storage tank. Regulation of the fluid level during the operation of the heat pump is enabled in particular by the disclosed device.

A height or a level of the fluid column (liquid column) of the working fluid in the condenser can hereby be used as a measure of the fluid level. Condensed working fluid typically collects during the operation of the heat pump at the bottom of the condenser, wherein the condensed working fluid in the condenser is supercooled by thermal contact with a heat sink. The fluid level is hereby provided by the height of the liquid column of the working fluid collected in the condenser.

When the fluid level is high, there is more condensed working fluid at the bottom of the condenser so that overall more working fluid is in thermal contact with the heat sink and consequently the working fluid is supercooled to a greater extent. The supercooling of the working fluid can thus be regulated by raising or lowering the fluid level. According to the disclosed device, it is possible to react to temperature fluctuations of the heat sink by regulating the supercooling of the working fluid in the condenser. In other words, the supercooling of the working fluid in the condenser can be adapted to the temperature fluctuations of the heat sink, the adaptation being effected in such a way that the heat pump always works in the most efficient way possible.

According to the prior art, known heat pumps in contrast comprise unregulatable supercooling of the working fluid because the fluid level in the condenser is more or less constant. Adaptation to the temperature fluctuations of the heat sink consequently does not take place according to the prior art.

By regulating the fluid level it is possible to react directly to fluctuations of the heat sink and/or a heat source by regulating the supercooling of the working fluid. Increased supercooling of the working fluid can hereby be advantageous because the enthalpy difference in the condenser is amplified by the increased supercooling of the working fluid. The COP and consequently the efficiency of the heat pump are advantageously raised as a result.

A further potential advantage is that large temperature fluctuations of the heat source and/or the heat sink can be regulated by means of a small change in the fluid quantity of the working fluid. As a result, there is no need for an oversized fluid filling quantity of the working fluid within the working circuit of the heat pump.

Moreover, in the case of operation using recuperators, superheating of a suction gas can advantageously be regulated by supercooling the working fluid.

Overall, the fluid level of the working fluid in the condenser of the heat pump is regulated by means of a piston and/or a diaphragm, as a result of which the supercooling of the working fluid is regulated and consequently the efficiency of the heat pump is improved in the event of temperature fluctuations of the heat sink.

In the disclosed method for operating a heat pump, a working fluid circulating within a working circuit of the heat pump is condensed by means of a condenser, is expanded by means of an expansion valve, is evaporated by means of an evaporator, and compressed by means of a compressor, wherein the working fluid is guided, with respect to the working circuit, between the condenser and the evaporator to a storage tank, wherein a fluid level of the working fluid in the condenser is regulated by means of a piston and/or a diaphragm of the storage tank.

In particular, the fluid level of the working fluid in the heat pump can be regulated by means of a translational movement of the piston and/or a displacement and/or a deformation of the diaphragm. Equivalent and similar advantages result for the already discussed device.

According to one embodiment, the storage tank which comprises a piston is fluidically coupled to the heat pump via an outlet and inlet valve, wherein the outlet valve is arranged, with respect to the working circuit, between the condenser and the expansion valve, and the inlet valve is arranged between the expansion valve and the evaporator.

Working fluid is thus advantageously guided to the storage tank downstream from the condenser and upstream from the expansion valve. This is therefore advantageous as the working fluid is at high pressure downstream from the compressor and upstream from the expansion valve. It is consequently possible to remove large quantities of working fluid for a short period of time from the working circuit and guide them to the storage tank.

The working fluid of the heat pump is temporarily stored in the storage tank in the liquid aggregate state. The working fluid is hereby preferably fed into the storage tank with the outlet valve open and the inlet valve closed. The fluid level is regulated by enlarging and/or reducing the storage volume (volume available for the working fluid in the storage tank) by means of a displacement of the piston in a straight line. As a result of enlarging the storage volume, it is consequently possible for more working fluid to be held in the storage tank, so that the fluid level in the condenser is reduced, and reduced supercooling of the working fluid occurs.

If the storage volume of the storage tank is now reduced by means of a displacement of the piston in a straight line, working fluid is guided from the storage tank, via the inlet valve, back into the working circuit of the heat pump so that the fluid level in the condenser is increased and consequently increased supercooling of the working fluid occurs. When the working fluid from the storage tank is fed back into the working circuit of the heat pump, it is expedient to close the outlet valve and open the inlet valve. During return into the working circuit of the heat pump, the working fluid can advantageously be caused to evaporate directly by displacement of the piston.

A storage tank which is designed as a hydraulic cylinder is hereby particularly preferred.

The storage tank can advantageously be formed technically in a simple fashion by a hydraulic cylinder, preferably by a double-action hydraulic cylinder. A pressure within the hydraulic cylinder of no more than 20 MPa is hereby preferred.

It can moreover be provided to lubricate an upper side of the piston with a compressor oil so that leaks at the piston of the hydraulic cylinder are not critical. As a result of the advantageous use of a hydraulic cylinder, when the evaporation and condensation temperature of the working fluid is the same, supercooling in the region of 5 K to 15 K can be achieved by means of a variation in the fluid level of the working fluid within the condenser.

In order to regulate the working fluid in the outlet or inlet valve, it can be provided that the said valves each comprise a further expansion valve and a non-return valve.

As a result, pressure differences between the working circuit of the heat pump and the storage tank can advantageously be compensated for.

In one embodiment, the storage tank is designed as a collecting tank, wherein the collecting tank comprises a diaphragm and the collecting tank is arranged, with respect to the working circuit, between the condenser and the expansion valve.

In particular, the collecting tank is consequently integrated directly in the working circuit of the heat pump. Hereby the working fluid of the heat pump collects in the collecting tank, wherein the amount of fluid of the working fluid collected in the collecting tank can be altered by means of the diaphragm. In other words, a first partial volume of the collecting tank, delimited by a deformation of the diaphragm, is enlarged or reduced, as a result of which a second partial volume (collection volume), which is available for the working fluid within the collecting tank, is reduced or enlarged.

If the supercooling of the working fluid in the condenser is increased, the first partial volume within the collecting tank is enlarged and consequently the second partial volume is reduced. If the supercooling is reduced, the first partial volume in the collecting tank is reduced by the diaphragm so that more liquid working fluid collects in the second partial volume of the collecting tank. By regulating the second partial volume (collection volume) which is available for the working fluid in the collecting tank by means of the diaphragm, the fluid level of the working fluid in the condenser is thus changed.

It is hereby particularly preferred to couple the collecting tank to an air compressor, wherein the air compressor is designed to feed compressed air into a partial volume, delimited by the diaphragm, of the collecting tank.

The deformation of the diaphragm and the consequent changing of the first or second partial volume of the collecting tank is advantageously regulated by means of feeding compressed air into the first partial volume delimited by the diaphragm. The first partial volume of the collecting tank is hereby enlarged when compressed air is fed in so that the second partial volume which is available for the working fluid within the collecting tank is reduced. Overall, the fluid level of the working fluid in the condenser can advantageously be regulated thereby.

The first partial volume is advantageously reduced by a compressed-air outlet valve which is coupled to the collecting tank.

If compressed air is removed from the first partial volume of the collecting tank via the compressed-air outlet valve coupled to the collecting tank, the first partial volume is reduced. By reducing the first partial volume, the second partial volume which is available for the working fluid in the collecting tank is enlarged. In other words, more working fluid thus collects in the collecting tank so that the supercooling of the working fluid in the condenser of the heat pump is reduced. By varying or regulating the feeding-in and release of compressed air, the supercooling of the working fluid is thus regulated.

According to one embodiment, the collecting tank comprises a displacement unit which is designed to mechanically displace the diaphragm.

The first partial volume is advantageously enlarged or reduced by displacing the diaphragm by means of the displacement unit. As a result, the fluid level of the working fluid in the condenser of the heat pump can in turn be regulated because the second volume (collection volume) is correspondingly reduced or enlarged. The air compressor and the outlet valve can advantageously be omitted in this embodiment.

According to one embodiment, the fluid level can be regulated by means of the piston and/or the diaphragm of the working fluid if the fluid level of the working fluid in the condenser falls below or exceeds a threshold value.

Because the fluid level of the working fluid in the condenser is positively correlated with the supercooling of the working fluid, the supercooling of the working fluid is advantageously regulated via regulating the fluid level. If the fluid level exceeds a specified level which corresponds, for example, to the threshold value for the fluid level, the working fluid may be supercooled too much. The fluid level of the working fluid must thus be lowered as part of the regulation. In the opposite case of the fluid level falling below the threshold level, the fluid level of the working fluid in the condenser can be raised by regulation so that the desired increased supercooling of the working fluid is set.

According to a further embodiment, the fluid level of the working fluid is regulated if the temperature of the working fluid exceeds or falls below a threshold value.

It is, for example, possible to detect the temperature of the working fluid and consequently the supercooling of the working fluid directly by measuring the temperature in the condenser. The temperature of the working fluid in the condenser is hereby typically indirectly proportional to the fluid level of the working fluid in the condenser. When the fluid level is high, there is a high degree of supercooling and hence a low temperature of the working fluid, whilst when the fluid level is low, the temperature is higher and hence the supercooling of the working fluid is lower. The temperature of the working fluid is consequently advantageously measured inside the condenser of the heat pump. Other points at which the temperature and/or the fluid level is measured in the working circuit of the working fluid can be provided.

FIG. 1 shows a device 1 which comprises a heat pump 4 and a storage tank 2, wherein the heat pump 4 has a condenser 6, an expansion valve 8, an evaporator 10, and a compressor 12. The heat pump 4 is hereby coupled to the storage tank 2 fluidically by means of a working fluid 24 of the heat pump 4 via an outlet valve 18 and via an inlet valve 20. The working fluid 24 circulates in the heat pump 4 in a working circuit 42.

In the exemplary embodiment of the device 1 shown in FIG. 1, the storage tank 2 is designed as a hydraulic cylinder 2 and comprises a piston 14. A storage volume 30 of the hydraulic cylinder 2 is hereby regulated by means of a straight-line movement of the piston 14, wherein the straight-line movement is illustrated in FIG. 1 by the directional arrows 32, 33. In other words, a first partial volume 30 which is available to the working fluid 24 in the hydraulic cylinder 2 is enlarged (directional arrow 33) or reduced (directional arrow 32) by means of the straight-line movement of the piston 14.

When the outlet valve 18 is opened and the inlet valve 20 is closed, the working fluid 24 condensed in the condenser 6 is fed into the hydraulic cylinder 2 downstream from the condenser 6 and upstream from the expansion valve 8 with respect to the working circuit 42 or with respect to a direction of the working circuit 42. The working fluid 24 is hereby advantageously fed into the hydraulic cylinder 2 upstream from the expansion valve 8 so that the working fluid 24 is fed into the hydraulic cylinder 2 at high pressure, for example within the range of 10 MPa to 20 MPa. As a result of the elevated pressure, large amounts of working fluid 24 can be removed from the working circuit 42 of the heat pump 4 and fed into the hydraulic cylinder 2 in just a short period of time. In other words, the mass flow of the working fluid 24 in the outlet valve 18 is increased as a result of the elevated pressure. Further expansion valves 21 and non-return valves 22 are provided for the outlet and inlet valves 18, 20 for regulation purposes.

The outlet valve 18 is closed and the inlet valve 20 opened in order to return the working fluid 24 into the working circuit 42 of the heat pump 4. The working fluid 24 is hereby forced out of the hydraulic cylinder 2 by a straight-line movement—indicated by the directional arrow 32. The working fluid 24 is returned, with respect to the working circuit 42, preferably downstream from the expansion valve 8 at a low pressure level. As a result, the working fluid 24 can advantageously be caused to evaporate directly.

If more working fluid 24 is now collected in the hydraulic cylinder 2 owing to an enlargement in the storage volume 30 by means of a movement of the piston 14—indicated by the directional arrow 33—the fluid level of the working fluid 24 in the condenser 6 falls. The lower the fluid level of the working fluid 24 in the condenser 6, the lower the degree of supercooling. The working fluid 24 thus leaves the condenser 6 more or less at a point on the boiling point curve and is thus in thermodynamic equilibrium with its vapor phase. In other words, the working fluid 24 is not supercooled, or only slightly.

Overall, the device 1 shown enables the fluid level of the working fluid 24 in the condenser 6 of the heat pump 4 to be regulated such that the supercooling of the working fluid 24 in the condenser 6 can be regulated. FIG. 2 shows a device 1 which comprises a heat pump 4 and a collecting tank 3, wherein the heat pump 4 has a condenser 6, an expansion valve 8, an evaporator 10 and a compressor 12. In the exemplary embodiment of the device 1 shown in FIG. 2, the collecting tank 3 comprises a diaphragm 16 which divides the total volume of the collecting tank 3 into a first and a second partial volume 30, 31.

A working fluid 24 circulating in a working circuit 42 of the heat pump 4 is collected in the second partial volume 31 (collection volume) of the collecting tank 3. The collecting tank 3 is arranged downstream from the condenser 6 and upstream from the expansion valve 8, with respect to the working circuit 42, and integrated directly into the working circuit 42 of the heat pump 4.

The first partial volume 30, which is delimited by the diaphragm 16, is enlarged by feeding in compressed air by means of an air compressor 26. Enlarging or reducing the partial volume 30 translates into a reduction or enlargement of the second partial volume 31. Hereby, the first partial volume 30 is reduced or the second partial volume 31 is enlarged by removing compressed air by means of a compressed-air outlet valve 28. If the first partial volume 30 is enlarged by feeding in compressed air by means of the air compressor 26, less working fluid 24 is collected in the collecting tank 3. Consequently more working fluid 24 collects in the condenser 6 of the heat pump 4. As a result, the working fluid 24 in the condenser 6 is supercooled to a greater degree because the fluid level in the condenser 6 is raised.

When the first partial volume 30 is reduced by removing compressed air by means of the compressed-air outlet valve 28, the second partial volume 31 is enlarged so that more working fluid 24 collects in the collecting tank 3. As a result, the fluid level of the working fluid 24 in the working circuit 42 of the heat pump 4 is reduced so that working fluid 24 is extracted from the condenser 6 and the supercooling of the working fluid 24 in the condenser 6 is reduced.

According to the prior art, known working fluids, for example R134a and/or R245fa, can be used as working fluids 24. Working fluids can preferably also be those which comprise at least one of the substances 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone (trade name Novec™ 649), perfluoromethyl butanone, 1-chloro-3,3,3-trifluoro-1-propene, cis-1,1,1,4,4,4-hexafluoro-2-butene, and/or cyclopentane. The use of R134a, R400C, and/or R410a can also be provided.

Although the invention has been illustrated and described in detail by the preferred exemplary embodiments, the invention is not limited by the disclosed example and other variations can be derived by a person skilled in the art without going beyond the protective scope of the invention. 

What is claimed is:
 1. A device, comprising: a storage tank; and a heat pump comprising: a condenser, an expansion valve, an evaporator, a compressor, a working circuit having a circulating working fluid, wherein the storage tank is arranged, with respect to the working circuit, between the condenser and the evaporator, and wherein the storage tank comprises at least one of a piston or a diaphragm that regulates a fluid level of the working fluid in the condenser.
 2. The device of claim 1, wherein the storage tank comprises a piston and is fluidically coupled to the heat pump via an outlet value and an inlet valve, wherein the outlet valve, with respect to the working circuit, is arranged between the condenser and the expansion valve, and the inlet valve is arranged between the expansion valve and the evaporator.
 3. The device of claim 2, wherein the storage tank comprises a hydraulic cylinder.
 4. The device of claim 2, wherein at least one of the outlet valve or the inlet valve comprises a further expansion valve and a non-return valve.
 5. The device of claim 1, wherein the storage tank is a collecting tank comprising a diaphragm, and wherein the collecting tank is arranged, with respect to the working circuit, between the condenser and the expansion valve.
 6. The device of claim 5, wherein the collecting tank is coupled to an air compressor, wherein the air compressor feeds compressed air into a partial volume of the collecting tank, the partial volume being delimited by the diaphragm.
 7. The device of claim 6, wherein the partial volume of the collecting tank is coupled to a compressed-air outlet valve.
 8. The device of claim 5, wherein the collecting tank includes a displacement unit configured to mechanically displace the diaphragm.
 9. A method for operating a heat pump with a working fluid circulating within a working circuit, the method comprising: condensing the working fluid using a condenser, expanding the working fluid using an expansion valve, evaporating the working fluid using an evaporator, and compressing the working fluid using a compressor, guiding the working fluid between the condenser and the evaporator to a storage tank, and regulating a fluid level of the working fluid in the condenser using at least one of a piston or a diaphragm of the storage tank.
 10. The method of claim 9, comprising: regulating the fluid level using the piston, and guiding the working fluid to the storage tank using an outlet valve.
 11. The method of claim 10, comprising guiding the working fluid from the storage tank back to the heat pump by closing the outlet valve and opening an inlet valve coupled between the expansion valve and the evaporate.
 12. The method of claim 9, wherein: the storage tank a collecting tank including a diaphragm that regulates the fluid level, and the working fluid is guided, with respect to the working circuit, between the condenser and the expansion valve to the collecting tank.
 13. The method of claim 12, wherein at least a partial volume of the collecting tank is enlarged or reduced by a mechanical displacement of the diaphragm.
 14. The method of claim 9, comprising regulating the fluid level of the working fluid if the fluid level of the working fluid in the condenser exceeds or falls below a threshold value.
 15. The method of claim 9, comprising regulating the fluid level of the working fluid if the temperature of the working fluid exceeds or falls below a threshold value. 